The invention generally relates to the field of rotary cutting machines, and more particularly, to an improved rotary bridge for use with such rotary cutting machines.
Rotary cutting machines are widely used in such industries as the printing or converting industry to cut, score and perforate cutting material such as paper, plastic, cardboard, non-wovens and the like. In general, these rotary cutting machines have two cooperating cylinders, one of which carries a rotary cutting die having a knife or cutting rule, and the other cylinder that acts as an anvil against which the knife bears as the paper is cut. Together, these cylinders help drive cutting material though the machine in order to be processed. The cutting edge of the knife and the surface of the anvil cylinder normally rotate at the same speed and the cutting material is cut as the cutting edge of the knife moves into and out of engagement with the anvil surface.
Rotary cutting dies have been manufactured and used for numerous years. The cutting rule extends above the surface of the rigid die plate and defines a cutting design. The design created by the metallic cutting rule is employed to cut the cutting material during the rotary cutting process.
Conventional rotary cutting dies may be mounted on discrete sections of a rotary cutting machine die cylinder. The die cylinder typically contains a number of receiving holes spaced at predetermined intervals. The receiving holes are positioned in an array along the die cylinder, and are configured to receive screws or other fasteners that extend through a rigid die plate of the rotary cutting die so as to affix the cutting die to the die cylinder. Mounting holes are bored into the die plate to align with the receiving holes in the die cylinder. The rotary cutting die is thus aligned and positioned on the die cylinder to reflect the predetermined pattern for the cutting, scoring or perforating process.
When the die plates are positioned on the die cylinder, there may be sections of the die cylinder that do not have a die plate attached, depending on the particular requirements of the cutting operation. Because the die plates typically have an associated thickness, an unevenness will form between the portions of the cylinder that have die plates attached and those that do not. If this unevenness is left on the cylinder, cutting material being processed may not be effectively driven through the rotary cutting machine. Instead, the cutting material may jam between the cylinders, thereby causing the machine to bind up and preventing the processing of cutting material, and may even lead to the breakage of the rotary cutting die. Stopping operations in order to correct these problems can be time consuming, inconvenient and expensive. Furthermore, this unevenness may cause cutting material to xe2x80x9cfly outxe2x80x9d from the rotary cutting machine as it is being processed, causing the cutting material to be delivered from the rotary cutting machine and onto a delivery table in an inconsistent and uncontrolled manner, requiring further processing before the cutting material is suitable for use.
One way to eliminate the unevenness is to use multiple layers of rubber or layers of rubber and velcro, stacked on top of each other, to fill in areas where die plates are not attached to the die cylinder. Typically, the layers are adhesively bound to each other, with the innermost layer being adhesively bound to the die cylinder. These stacked layers often need to achieve an overall thickness of the order of ⅝ of an inch, the thickness of a typical die plate. However, rubber has a tendency to degrade when it is layered to a large thickness because the layers are subject to large amounts of tension. The inner surfaces of the stacked layers are compressed, and the outer surfaces are expanded. Therefore, the high rotational speeds the die cylinder typically achieves when in operation, in conjunction with a large expansion of the outer layers of rubber, may cause the rubber to peel or break off from the die cylinder. This can lead to cutting material becoming jammed between the cylinders, causing the problems described above. Furthermore, adhering layers of velcro and/or rubber to the die cylinder may be time consuming.
Another common method used to fill in the areas where die plates are not attached to the die cylinder is to use a bridge manufactured from a rigid, epoxy-base material, mounted to the cylinder die via screws passing through mounting holes on the bridge and the receiving holes of the die cylinder. However, bridges made of an epoxy-base material may be difficult to radially size to fit on a die cylinder. Generally, bridges must be sized to fit on the die cylinder. In particular, each bridge must be manufactured with a mounting radius that precisely matches the radius of the die cylinder on which the bridge is to be mounted. Precise matching of the bridge to the die cylinder is necessary to insure that gaps are not left between the bridge and the die cylinder. As mentioned above, imprecise or inaccurate matching may lead to cutting material becoming jammed between the cylinders, and may lead stress wear that could result in the breakage of the bridge or rotary cutting die.
Manufacturing a bridge made of epoxy-base materials to precisely match the die cylinder can be difficult because epoxy-based materials tend to shrink during the manufacturing process, thereby altering the radius or distorting the shape of the bridge. Moreover, it is nearly impossible to predict the shrinkage of the epoxy-based bridge with any precision. In addition to the problems cited above, shrinkage of the bridge material may create internal stresses that may compromise the integrity of the bridge.
Additionally, if the radius of the bridge does not precisely match the radius of the die cylinder, then the bridge must be xe2x80x9cflexedxe2x80x9d to fit onto the die cylinder. In other words, the bridge must be xe2x80x9cflexedxe2x80x9d or bent so as to eliminate any gaps between the bridge and the die cylinder. The rigidity of the epoxy-base material, however, will prevent any appreciable xe2x80x9cflexingxe2x80x9d of the bridge. If the bridge cannot be xe2x80x9cflexedxe2x80x9d sufficiently to fit onto the die cylinder, then the bridge is typically discarded.
In the event that the bridge is xe2x80x9cflexedxe2x80x9d to fit onto the die cylinder, additional mounting fasteners or clamps will usually be required to secure and hold the bridge against the die cylinder. These additional mounting fasteners will necessarily require the installation of additional receiving holes in the die cylinder.
xe2x80x9cFlexingxe2x80x9d of the bridge to fit the die cylinder may also cause adverse stresses in the bridge. Because epoxy-base materials are typically brittle, these adverse stresses may lead to the fracturing or shattering of the bridge. Moreover, a dangerous situation may be created if the bridge shatters. Shattered pieces of the bridge may be propelled outwardly from the die cylinder.
Furthermore, stacked layers and epoxy-based bridges are difficult to reconfigure for different processing operations. Generally, for a first type of cutting operation, a predetermined number of rotary cutting dies will be mounted to the die cylinder in a predetermined configuration. Stacked layers or epoxy-base bridges will be attached to the die cylinder in the areas where the rotary cutting die is not so attached. When the first operation is finished, a second type of operation may be begun. However, when a different operation is begun, the configuration of the rotary cutting dies on the die cylinder, the number of rotary cutting dies required, or both, may change. If this occurs, the shape and size of the areas on the die cylinder for mounting stacked layers or bridges will change. Because stacked layers are adhesively bound to the die cylinder, reshaping them to accommodate the second operation may be time consuming, messy, and may tear the layers. Epoxy-base materials, on the other hand, will generally be too brittle to reshape.
Accordingly, it would be desirable to have a bridge that overcomes the disadvantages and limitations described above.
In view of the above, the present invention provides a unique rotary bridge assembly that overcomes the disadvantages and limitations described above. According to a first aspect of the present invention, the bridge assembly includes a urethane-base flexible bridge die having an inner surface and an outer surface. The bridge die is formed for use on a discrete section of a rotary die cylinder and is used with at least one rotary cutting die mounted to the rotary die cylinder. The bridge die has at least one score so that the bridge assembly may be resized by removing a portion of the bridge assembly at the score. A plurality of rubber strips are also included and are attached to the outer surface of the bridge die.
Another aspect of the bridge assembly provides a urethane-base flexible bridge die being formed of a polyurea elastomer material having a hardness of 60xc2x15 (Shore D) and being sized for use on a discrete section of a rotary die cylinder.
Another aspect of the bridge assembly provides a urethane-base flexible bridge die being of a polyurea elastomer having a hardness of 60xc2x15 (Shore D). The bridge die has an inner surface, an outer surface, a plurality of scores, and a plurality of mounting holes. The plurality of scores allows the bridge assembly to be resized by removing a portion of the bridge assembly at a score. The plurality of mounting holes passes through the inner surface and the outer surface and are for mounting the bridge assembly to a rotary die cylinder. The bridge die is yellow in color and is sized for use on a discrete section of the rotary die cylinder. A plurality of rubber strips are attached to the outer surface of the bridge die and are at least {fraction (1/16)} inches thick. The bridge die and the rubber strips together form a thickness that is at least {fraction (3/16)} inches.
Another aspect of the invention includes a rotary cutting machine. The rotary cutting machine includes a rotary die cylinder, an anvil cylinder, at least one rotary cutting die, and at least one bridge assembly. The rotary cutting die includes a cutting rule and is formed for use on and mounted to a discrete section of the rotary die cylinder. The bridge assembly is formed for use on the remaining sections of the rotary die cylinder and mounted to the rotary die cylinder. Together, the rotary die cylinder and the anvil cylinder drive a cutting material between them for processing by the cutting rule.
The preferred embodiment of the invention includes features in addition to those listed above. Moreover, the advantages over the current art discussed above are directly applicable to the preferred embodiment, but are not exclusive. The other features and advantages of the present invention will be further understood and appreciated when considered in relation to the detailed description of the preferred embodiment.